The measurement of cosmic distances is like a scaffold, where levels are built upon the structure below. To measure the distances to far galaxies, astronomers must calibrate their measurements using closer objects that we know the distance to; those in turn must be calibrated by closer objects still. As a result, if we are to trust the measurements we've made of the structure and expansion of the Universe, we'd better have really good measurements to nearby galaxies.

For that reason, astronomers have devoted a lot of effort to measuring the distance to the Milky Way's brightest satellite galaxy, Large Magellanic Cloud. Now G. Pietrzyński and colleagues have determined that galaxy's distance with unprecedented accuracy. By identifying a set of rare binary stars, their properties allowed the astronomers to measure their distances from Earth to 2.2 percent accuracy. These results will help refine the measurements on which cosmology is founded: the expansion rate of the Universe.

Distances within the Solar System can be measured a number of ways, including direct methods like radar ranging. With a truly accurate estimate of the size of Earth's orbit, astronomers can use parallax—the apparent displacement of stars in the sky as Earth orbits the Sun—to find the distances to stars in the Milky Way. Some stars are variable, changing brightness in a predictable way; these provide a means of measuring how far it is to neighboring galaxies.

These and other measurements allow astronomers to calibrate distances to galaxies containing Type Ia supernovae. These explosions are visible billions of light-years away, and outshine everything else in their host galaxies. As acknowledged by the 2011 Nobel Prize in physics, Type Ia supernovae are currently our best way to track the expansion rate of the Universe.

The current study provides a possible alternative means to measure distances on an intermediate scale with more accuracy than we can get using variable stars. The Large Magellanic Cloud (LMC) is the second-closest galaxy to the Milky Way; you can think of it as the second layer of scaffolding, above measurements inside our galaxy. (Only the Sagittarius dwarf spheroidal galaxy is closer than the LMC, but it's much smaller and fainter, and therefore less useful for cosmological calibrations.)

The researchers used data from the Optical Gravitational Lensing Experiment (yes, it's nicknamed OGLE), which was designed to look for fluctuations in dark matter density by observing stars in the LMC. While OGLE hasn't succeeded in its primary goal of spotting clumps of dark matter, it has amassed a lot of data from 35 million stars, going back as far as 1992.

From those 35 million stars, the astronomers identified 12 eclipsing binary stars; of those, they analyzed data from eight pairs for a period of eight years. These pairs they chose are rare, consisting of stars in the helium-burning stage, which occurs after they have exhausted their core's hydrogen fuel. Aging stars of this type have well-known intrinsic brightness in relation to their color.

The researchers also selected the eight binaries for the length of their orbits: relatively long periods ranging between 60 and 772 days. Combined with the amount of light blocked during the eclipses, these long orbits enabled the astronomers to reconstruct the sizes of the stars through the same techniques that are commonly used for spotting exoplanets. That provided a detailed physical picture of the binary star systems, pinpointing their exact intrinsic brightness to approximately 2 percent accuracy. If an object's intrinsic brightness is known, it's a remarkably simple matter to estimate its distance from Earth based on how much of that light reaches us.

The LMC has a fairly simple structure—a flattened disk—and all the binaries were found close to the galaxy's center. As a result, the astronomers used the stars' distances to estimate how far the LMC's center is from Earth: 49.97 kiloparsecs, give or take 0.19 kiloparsecs. (One kiloparsec is a thousand parsecs, or roughly 3,300 light-years.) That accuracy is about 2.2 percent, a vast improvement over previous estimates based on variable stars, which did no better than 8 percent.

With these estimates in hand, it will be possible to calibrate the expansion rate of the Universe—a quantity known as the Hubble parameter—to about 3 percent accuracy. Future observations should be able to improve both the LMC distance measurement and the Hubble parameter even further.

Stars don't "burn" anything... contrary to the title of this article. Burning is a chemical reaction. Stars fuse helium. Which is a nuclear reaction.

You're commenting on an English idiom. The helium is fuel for the star's reaction, and it stops being helium in the process. "Burning fuel" is a common idiom for anything that uses the fuel, regardless of the specific operation of use.

Stars don't "burn" anything... contrary to the title of this article. Burning is a chemical reaction. Stars fuse helium. Which is a nuclear reaction.

You're commenting on an English idiom. The helium is fuel for the star's reaction, and it stops being helium in the process. "Burning fuel" is a common idiom for anything that uses the fuel, regardless of the specific operation of use.

Yes, but even more than that - the result of the consumption of the fuel by nuclear reactions is *so* similar to what happens in chemical reactions that it makes more sense to think of it all as combustion. The math is exactly the same; you can get flames, and detonations, and (as in the case of a star) quiet simmering, with the only difference being that the reactions are strong/weak force mediated rather than electromagnetic. Thermal conduction, species diffusion, buoyancy, it all plays out the same way. So other than a preference for the kind of combustion we're (thankfully) more familar with, chemical combustion, there's no reason to call one form "burning" and the other not.

My consideration is not for the citizens of Ars Technica, but rather the general public linked to the site via news aggregations sites (this is currently the top article on Google News in the science section). In my opinion though, and I'm surprised that more of you aren't on board, is that if a less ambiguous term is available... use it. Call it a pet peeve if you like.

We don't say that humans 'burn' food. We say they 'digest' it.

ljdursi wrote:

tyrsius wrote:

fieyr wrote:

Stars don't "burn" anything... contrary to the title of this article. Burning is a chemical reaction. Stars fuse helium. Which is a nuclear reaction.

You're commenting on an English idiom. The helium is fuel for the star's reaction, and it stops being helium in the process. "Burning fuel" is a common idiom for anything that uses the fuel, regardless of the specific operation of use.

Yes, but even more than that - the result of the consumption of the fuel by nuclear reactions is *so* similar to what happens in chemical reactions that it makes more sense to think of it all as combustion. The math is exactly the same; you can get flames, and detonations, and (as in the case of a star) quiet simmering, with the only difference being that the reactions are strong/weak force mediated rather than electromagnetic. Thermal conduction, species diffusion, buoyancy, it all plays out the same way. So other than a preference for the kind of combustion we're (thankfully) more familar with, chemical combustion, there's no reason to call one form "burning" and the other not.

Because it is prone to misunderstanding. Just like saying a star burns is prone to misunderstanding for people whose everyday experience consists of burning of the non-nuclear variety. Also, I imagine things that you and I might consider as 'understood' are fairly annoying to someone trying to learn English.

tyrsius wrote:

fieyr wrote:

^We should probably stop doing that.

Why? Its perfectly understandable to most people. It doesn't need to be scientifically accurate, its understood.

I don't have a big issue with those uses honestly. I just think science articles, talking about scientific processes, should do their best to use the most appropriate scientific terms given the context.

styron wrote:

fieyr wrote:

Stars don't "burn" anything... contrary to the title of this article. Burning is a chemical reaction. Stars fuse helium. Which is a nuclear reaction.

I don't have a big issue with those uses honestly. I just think science articles, talking about scientific processes, should do their best to use the most appropriate scientific terms given the context.

I like the idea of specific words for specific ideas, so while I agree in principle, the fact is, average intelligence is low enough that the barrier of unfamiliar terms can and will turn away those who don't self select.

I see it as similar to the argument in the 90s: OH MY GOD KIDS ARE READING HORROR STORIES RL STINE IS THE DEVIL. Well, at least they are READING.

Better to get someone interested in the overview and say, wow, that's really cool, how do I learn more, than to turn them off with vagaries of language.

Yeah point taken, I completely agree. If burning stars are more exciting that fusing stars, and results in more interest, sure why not. I'm still a little concerned that the vagaries of language might themselves create a barrier, however as long as the vagaries aren't flat out wrong, then I guess we can afford a little leeway if the net effect is increased public interest. The article isn't a scientific paper or journal, and probably shouldn't be treated as such.

+1 to you for changing my mind.

Tom Brokaw wrote:

fieyr wrote:

I don't have a big issue with those uses honestly. I just think science articles, talking about scientific processes, should do their best to use the most appropriate scientific terms given the context.

I like the idea of specific words for specific ideas, so while I agree in principle, the fact is, average intelligence is low enough that the barrier of unfamiliar terms can and will turn away those who don't self select.

I see it as similar to the argument in the 90s: OH MY GOD KIDS ARE READING HORROR STORIES RL STINE IS THE DEVIL. Well, at least they are READING.

Better to get someone interested in the overview and say, wow, that's really cool, how do I learn more, than to turn them off with vagaries of language.

Ah, reading an article like this make me feel proud of my species of clever east african plains apes. Reading the comments makes me think we should be reclassified as species Pan Human instead of all that sapiens sapiens nonsense.

It's been interesting seeing all you experienced posters dogpile onto Fieyr the poor newbie, but he does have a point. I mean, ok let's not tech the techy tech, but at the same time it wouldn't hurt to have a line saying something like 'burning helium, consuming their remaining helium through ravening nuclear fusion until there's none left and the star explodes'. I'm no professional writer but Ars is, and science writing can be all of accessible, edificatory *and* exciting